1. Field of the Invention
The present invention relates to an ink-jet recording head configured such that a vibration plate partially constitutes a pressure generating chamber communicating with a nozzle orifice, through which a droplet of ink is ejected, and such that a piezoelectric element is provided via the vibration plate so as to eject a droplet of ink through displacing movement thereof, as well as to an ink-jet recording apparatus using the head.
2. Description of the Related Art
An ink-jet recording head is configured such that a vibration plate partially constitutes a pressure generating chamber communicating with a nozzle orifice, through which a droplet of ink is ejected, and such that a piezoelectric element causes the vibration plate to be deformed, thereby pressurizing ink contained in the pressure generating chamber and thus ejecting a droplet of ink through the nozzle orifice. Ink-jet recording heads which are put into practical use are classified into the following two types: an ink-jet recording head that employs a piezoelectric actuator operating in longitudinal oscillation mode; i.e., expanding and contracting in the axial direction of a piezoelectric element; and an ink-jet recording head that employs a piezoelectric actuator operating in flexural oscillation mode.
The former recording head has an advantage in that a function for changing the volume of a pressure generating chamber can be implemented through an end face of a piezoelectric element abutting an vibration plate, thereby exhibiting good suitability to high-density printing. However, the former recording head has a drawback in that the fabrication process is complicated; specifically, fabrication involves a difficult process of dividing the piezoelectric element into comb-tooth-like segments at intervals corresponding to those at which nozzle orifices are arranged, as well as a process of fixing the piezoelectric segments in such a manner as to be aligned with corresponding pressure generating chambers.
The latter recording head has an advantage in that piezoelectric elements can be formed on an vibration plate through a relatively simple process; specifically, a green sheet of piezoelectric material is overlaid on the vibration plate in such a manner as to correspond in shape and position to a pressure generating chamber, followed by firing. However, the latter recording head has a drawback in that a piezoelectric element must assume a certain amount of area in order to utilize flexural oscillation, thus involving difficulty in arranging pressure generating chambers in high density.
In order to solve the drawback of the latter recording head, as disclosed in, for example, Japanese Patent Application Laid-Open (kokai) No. 5-286131, the following process has been proposed. An even layer of piezoelectric material is formed on the entire surface of an vibration plate by use of a film deposition technique. By means of lithography the layer of piezoelectric material is divided in such a manner as to correspond in shape and position to pressure generating chambers, thereby forming independent piezoelectric elements corresponding to the pressure generating chambers.
In recent years, in order to realize higher-quality printing, ink-jet recording heads have been required to arrange nozzle orifice s at higher density.
However, in order to arrange nozzle orifices in high density, pressure generating chambers must be arranged in high density. High-density arrangement of pressure generating chambers causes reduction in the thickness of a compartment wall between pressure generating chambers, resulting in insufficient rigidity of a compartment wall and thus causing cross talk between adjacent pressure generating chambers.
In view of the foregoing, an object of the present invention is to provide an ink-jet recording head allowing high-density arrangement of pressure generating chambers and capable of preventing cross talk, as well as an ink-jet recording apparatus using the head.
To achieve the above object, the present invention provides an ink-jet recording head comprising a passage-forming substrate, an vibration plate, and a plurality of piezoelectric elements provided on one side of the passage-forming substrate via the vibration plate, the passage-forming substrate having a plurality of pressure generating chambers formed therein in such a manner as to communicate with corresponding nozzle orifices and as to be separated from one another by means of a plurality of compartment walls, the plurality of piezoelectric elements each comprising a lower electrode, a piezoelectric layer, and an upper electrode. The vibration plate undergoes tensile stress; the number n of the pressure generating chambers arranged per inch is more than 200 and is related to width w of the pressure generating chamber and thickness d of the compartment wall as represented by (w+d)=1 inch/n; and the thickness d of the compartment wall is more than 10 xcexcm and is related to thickness h of the passage-forming substrate as represented by (dxc3x973)xe2x89xa6hxe2x89xa6(dxc3x976).
Through employment of the above features, even when the pressure generating chambers are arranged in relatively high density, the rigidity of the compartment walls can be maintained, whereby good ink ejection characteristics can be maintained.
The thickness h of the passage-forming substrate and the thickness d of the compartment wall may be related as represented by (dxc3x974)xe2x89xa6hxe2x89xa6(dxc3x975).
Through employment of the above feature, the rigidity of the compartment walls can be reliably maintained, whereby good ink ejection characteristics can be maintained at all times.
The percentage of compliance of the compartment wall to that of the pressure generating chamber may be not greater than 10%.
Since the percentage of compliance of the compartment wall is relatively low, the influence of cross talk can be reduced to a low level.
The thickness h of the passage-forming substrate may be more than the width w of the pressure generating chamber.
Employment of the above feature restrains a change in characteristics, which would otherwise result from an error in the thickness h of the passage-forming substrate.
Crystals of the piezoelectric layer may assume preferred orientation.
Since the piezoelectric layer is formed by a thin film deposition process, crystals assume preferred orientation.
Crystals of the piezoelectric layer may assume preferred orientation with respect to (100) planes.
When the piezoelectric layer is formed by a predetermined thin film deposition process, crystals assume preferred orientation with respect to (100) planes.
Crystals of the piezoelectric layer may be rhombohedral.
When the piezoelectric layer is formed by a predetermined thin film deposition process, crystals become rhombohedral.
Alternatively, crystals of the piezoelectric layer may bexe2x80x94columnar.
When the piezoelectric layer is formed by a thin film deposition process, crystals become columnar.
The piezoelectric layer may assume a thickness of 0.5 xcexcm to 2 xcexcm.
Since the thickness of the piezoelectric layer is relatively small, patterning in high density becomes possible.
The sum of the stress of the vibration plate and stresses of component layers of each of the piezoelectric elements may be equivalent to tensile stress.
Through employment of the above feature, a restraint which is induced at the vibration-plate-side end of each compartment wall by stresses of the piezoelectric elements and vibration plate prevents cross talk.
The sum of the stress of the vibration plate and stress of the lower electrode may be equivalent to tensile stress.
Through employment of the above feature, stresses of the vibration plate and lower electrodes function to more reliably restrain the compartment walls, thereby reliably preventing cross talk.
The piezoelectric layer may undergo tensile stress.
Through employment of the above feature, stress of the piezoelectric layer functions to more reliably restrain the compartment walls, thereby reliably preventing cross talk.
The vibration plate may comprise a compression layer undergoing compression stress on the side facing the pressure generating chambers.
Even though the vibration plate includes a compression layer, if stress of the vibration plate on the whole is tensile stress or if the sum of the stress of the vibration plate and stresses of component layers of each of the piezoelectric elements is equivalent to tensile stress, cross talk can be prevented.
When the pressure generating chambers are formed, the piezoelectric elements may be convexly warped toward corresponding pressure generating chambers.
Through employment of the above feature, stress of the vibration plate functions to more reliably prevent cross talk.
The passage-forming substrate may be formed of a monocrystalline silicon substrate and may be formed to a predetermined thickness through the other side thereof being polished.
Through employment of the above feature, the thickness of the passage-forming substrate can be reduced by means of polishing in a relatively easy manner.
The passage-forming substrate may be formed of a monocrystalline silicon substrate and may be formed to a predetermined thickness through a previously provided sacrificial substrate being removed from the other side thereof.
Through employment of the above feature, a relatively thin passage-forming substrate can be formed in a relatively easy manner.
The pressure generating chambers may be formed through anisotropic etching, and component layers of the piezoelectric elements may be formed through film deposition and lithography.
Employment of the above features allows formation of the pressure generating chambers with high precision and in high density in a relatively easy manner.
The present invention also provides an ink-jet recording apparatus comprising an ink-jet recording head as described above.
An ink-jet recording apparatus using an ink-jet recording head of the present invention can achieve high-speed, high-quality printing.